Use of ammonium sulphate as a sulphur fertilizer: Implications for ammonia volatilization

Abstract

Abstract Ammonium sulphate is widely used as a sulphur (S) fertilizer, constituting about 50% of global S use. Within nitrogen (N) management, it is well known that ammonium‐based fertilizers are subject to ammonia (NH 3 ) volatilization in soils with pH > 7, but this has been overlooked in decision making on S fertilization. We reviewed 41 publications reporting measurements of NH 3 loss from ammonium sulphate in 16 countries covering a wide range of soil types and climates. In field experiments, loss was mostly <5% of applied N in soils with pH (in water) <7.0. In soils with pH > 7.0, there was a wide range of losses (0%–66%), with many in the 20%–40% range and some indication of increased loss (ca. 5%–15%) in soils with pH 6.5–7.0. We estimate that replacing ammonium sulphate with a different form of S for arable crops could decrease NH 3 emissions from this source by 90%, even taking account of likely emissions from alternative fertilizers to replace the N, but chosen for low NH 3 emission. For every kt of ammonium sulphate replaced on soils of pH > 7.0 in temperate regions, NH 3 emission would decrease from 35.7 to 3.6 t NH 3 . Other readily available sources of S include single superphosphate, potassium sulphate, magnesium sulphate, calcium sulphate dihydrate (gypsum), and polyhalite (Polysulphate). In view of the large areas of high pH soils globally, this change of S fertilizer selection would make a significant contribution to decreasing NH 3 emissions worldwide, contributing to necessary cuts to meet agreed ceilings under the Gothenburg Convention.

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